Increased Potassium Absorption Confers Resistance to Group IA Cations in Rubidium-Selected Suspension Cells of Brassica napus

Abstract

Cell lines of suspension cultures of Brassica napus cv. Jet Neuf were identified for their ability to tolerate 100 millimolar Rb+, a level which was double the normally lethal concentration. Ten spontaneous isolates were obtained from approximately 5 x 10' cells, one of which was reestablished as a cell suspension. This cell line, JL5, was also resistant to the other group IA cationsLi, Na+, K+, and Cs+-and this trait was stable for at least 30 cell generations in the absence of Rb+ selection pressure. The growth characteristics were similar to those of sensitive cells under nonselective conditions. The selected JL5 cells were shown by analysis to have effected more net accumulation of K and Rb+ and less of Na+ than did the unselected cells. JL5 and unselected cells after 14 days of culture in basal medium contained 597.2 and 258.2 micromoles of K per gram dry weight, respectively. Michaelis-Menten kinetic analysis of K+ influx showed that JL5 possessed an elevated phase 1 V,,,e, but there was no alteration in its Km. This is the first time that a plant mutation has been shown to have both increased influx and net absorption of a major essential cation.Salt-tolerant cultures have been isolated from a number of plant species (1-3, 15, 21) including Brassica napus (7). Selections that have employed sodium salts often resulted in the isolates being resistant to water stress where the tolerance mechanism appears to have a broader physiological basis than that involved solely in the membrane transport and cellular compartmentation of Na+. This study was specifically designed to identify cells possessing alterations in K+ absorption. It

Mutants of Arabidopsis thaliana Capable of Germination under Saline Conditions

“…1, B-F). Li+ was included in the study because its accumulation by plant cells is similar to that of Na+, but it is much more toxic (Lefebvre, 1989). Unlike NaCl, the increasing concentrations of KCl, LiCl, and K2S04 had similar effects on the germination of WT and mutant lines.…”

“…An innate ability to sequester Na+ in the vacuole to a greater extent than K+ could account for no significant improvement in tolerances for salts of the latter ion, especially if C1-partitioning follows suit. K salts have been shown to be more toxic than Na ones in WT cell cultures of Brassica napus (Lefebvre, 1989). A mutant of this cell line was resistant to elevated NaCl and KCl concentrations because of an increased ability to accumulate K+, presumably in the vacuole.…”

Molecular determinants of the Arabidopsis AKT1 K+ channel ionic selectivity investigated by expression in yeast of randomly mutated channels

“…Physiological akpproaches have revealed that Na + can be a competitive inhibitor of K + uptake in roots ( Rains and Epstein 1967), and molecular data regarding interactions of K + and Na + in plant transporters have recently been reported ( Rubio et al 1995; Santa‐Maria et al 1997; Fu and Luan 1998). Interestingly, increased K + ‐uptake capacity and K + accumulation correlate with increased salt tolerance in many experimental systems ( Rush and Epstein 1981; Lefebvre 1989; Watad et al 1991; Taleisnik and Grunberg 1994). Thus, elucidating the molecular mechanisms allowing selective transport of K + in plants might help to improve the salt tolerance of crop plants ( Schroeder et al 1994).…”

Changes in growth variables and potassium content in leaves of Black Barley in response to NaCl

“…In the present study three parameters can clearly distinguish Black and Arivat; these included growth rate and duration of cell division, and K + content of leaves, the parameters that have been considered as promising crucial keys in developing salt tolerant crops (Rao, 1986;Lefebvre, 1989;Zhu et al, 1998;Flowers, 2004). However, a huge number of published works over the last five decades have confirmed that the presence of sodium salts in the soil would prevent the absorption of potassium, thereby plants might suffer from K + deficiency (Yasseen, 1983;Botella et al, 1997;Mengel et al, 2001;Shabala and Cuin, 2007).…”

“…Such a conclusion could be valid for Arivat, as shown by the data of the ionic content, since na + competes with K + for major binding sites in many key metabolic processes in the cytoplasm, such as enzymatic reactions, protein synthesis and ribosome functions, and more than 50 cytoplasmic enzymes are activated by K + (Benlloch et al, 1994;Marschner, 1995). The growing bulk of evidence has demonstrated that the ability of a plant to retain K + in the cytosol may be crucial in achieving increased salt tolerance (Lefebvre, 1989;Zhu et al, 1998;Rascio et al, 2001). Scientists are trying to develop crop plants (like cereals) that have efficient mechanisms to maintain high levels of potassium in leaves under salt stress (Zhu et al, 1998;Schachtman and Liu, 1999;Shabala and Cuin, 2007).…”